JPS59172138A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a magnetic layer which is excellent in the dispersibilty and dispersion stability of magnetic powder, has good surface smoothness and has an excellent electrical characteristics by incorporating high mol.wt. poly(acrylic acid/propylene glycol ester of acrylic acid) surface active agent in the magnetic layer. CONSTITUTION:Magnetic powder and high mol.wt. poly(acrylic acid/propylene glycol ester of acrylic acid) surface active agent are incorporated in a magnetic layer. The high mol.wt. poly(acrylic acid/propylene glycol ester of acrylic acid) surface active agent is expressed by the formula and is used preferably in a range of 0.1-10wt% to the magnetic powder. The high mol.wt. poly(acrylic acid/ propylene glycol ester of acrylic acid) surface active agent is soluble in water and when said agent contacts with the magnetic powder dispersed in an aq. soln., the agent sticks satisfactorily on the particle surfaces and forms a film, by which the dispersibility and dispersion stability of the magnetic powder are improved and the surface smoothness and electrical characteristics of the magnetic layer are improved.

Description

Detailed Description of the Invention The present invention relates to a magnetic recording medium, and its object is to have a magnetic layer having excellent dispersibility and dispersion stability of magnetic powder, good surface smoothness, and excellent electrical properties. The purpose of this invention is to provide a magnetic recording medium.

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
The magnetic layer is required to have good surface smoothness, excellent electrical properties, and excellent durability.

Therefore, the magnetic powder used has excellent dispersibility, and the surface smoothness of the magnetic layer is good, making it possible to provide magnetic recording media with high sensitivity and high S.
It is desirable to have something that can provide excellent electrical properties such as N ratio and improve durability, but because ordinary magnetic powder has a hydrophilic surface, it is difficult to disperse it well in a hydrophobic binder component. However, the dispersibility of the magnetic powder is not sufficiently good and tends to aggregate easily.

Therefore, in order to improve the dispersibility of magnetic powder, attempts have been made to improve the dispersibility of magnetic powder by, for example, treating the magnetic powder with a dispersant such as a dialkyl sulfosuccinate. In addition, this type of dispersant has a high foaming property and generates a large amount of bubbles when dispersing magnetic powder, making it difficult to work with.

The inventors conducted various studies in view of the current situation, and found that the dispersibility and dispersion stability of magnetic powder can be improved by incorporating a poly(acrylic acid-acrylic acid propylene glycol ester)-based high 314 surfactant into the magnetic layer. The inventors have discovered that the magnetic layer has a sufficiently improved surface smoothness, and the electrical properties of the magnetic layer are further improved, leading to the creation of this invention.

The poly(acrylic acid-acrylic acid propylene glycol ester)-based high molecular weight surfactant used in this invention has the general formula (where M, , M2 is H or NH4 or an alkali metal, and n is an integer of 2 to 400. An ester of acrylic acid or its salt and propylene glycol acrylate represented by For example, Neatorol 42 manufactured by the company.

Natrol 42 [Poly (sodium acrylate propylene glycol acrylate ester)] This type of poly (acrylic acid - propylene glycol acrylate ester) based high molecular weight surfactant is water-soluble and has a magnetic powder dispersed in an aqueous solution. When in contact, it adheres well to the particle surface and forms a film, sufficiently improving the dispersibility and dispersion stability of the magnetic powder, improving the surface smoothness of the magnetic layer, and further improving the electrical properties. .

In order to incorporate such poly(acrylic acid-acrylic acid propylene glycol ester)-based high molecular weight surfactants into the magnetic layer, they are dissolved in water, and dried magnetic powder is added to this aqueous solution to form a magnetic layer. An aqueous dispersion of a magnetic powder produced by surface-treating the powder or by mixing an aqueous solution of iron or other metal salt with an aqueous alkaline solution is used as it is, and in this aqueous dispersion, The magnetic powder is surface-treated by adding a poly(acrylic acid-acrylic acid propylene glycol ester) based high molecular weight surfactant, and after drying, this magnetic powder is used to prepare a magnetic paint. The amount used is preferably within the range of 0.1 to 10% by weight based on the magnetic powder; if it is too small, the desired effect will not be obtained, and if it is too large, the surface smoothness of the magnetic layer will deteriorate.

As the magnetic powder used in this invention, for example, TFe
In addition to 203 powder, Fe3O4 powder, co-containing rFe2O3 powder, and co-containing Fe5Q4 powder, various conventionally known magnetic powders such as metal powders such as Fe powder, co powder, and Fe-Ni powder are widely included.

In addition, as the binder resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin,
Any conventionally widely used binder resin such as polyurethane resin or isocyanate compound can be used.

Examples of organic solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and sulfoxide solvents such as dimethyl sulfoxide. , ether solvents such as tetrahydrofuran, dioxane, etc.
Solvents suitable for dissolving the binder resin used may be used alone or in a mixture of two or more without particular restrictions.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, etc. may be added as appropriate.

Next, embodiments of the invention will be described.

Example 1 Acicular r-Fe203 powder 1800g Cobalt sulfate (CO3O4.7H20) 600g Ferrous sulfate (FeSO+7H20) 1800g Caustic soda 2128g After reacting dispersion 18β containing the above components at 45°C for 8 hours,
Washed with water and filtered. Next, Nateroll 42 [Poly (manufactured by Kanebo NSC)] was added to the obtained slurry.
Add 30β of an aqueous solution containing 100g of sodium acrylate and propylene glycol ester of acrylate, and
After time dispersion treatment, dry and cobalt-containing γ-1”e
203 magnetic powder was obtained. The obtained cobalt-containing y-F
The amount of Neatorol 42 deposited on the e203 magnetic powder was 35 .mu./g. Using the thus obtained cobalt-containing γ-Fe203 magnetic powder, 100 parts by weight of Co-containing r-Fe203 magnetic powder (coating amount of Netrol 42 35 μg/g) was manufactured by VAGH (US company U, C, C). 18 (vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Takelac E-551T 12 (manufactured by Narita Pharmaceutical Co., Ltd., polyurethane elastomer) Desmod Shikaku Bayer 3 (manufactured by Narita Pharmaceutical Co., Ltd., trifunctional low molecular weight isocyanate compound) Laurin Acid 2 Cyclohexanone 80 Toluene
A magnetic paint was prepared by mixing and dispersing a mixture having a composition of 80% in a ball mill for about 100 hours. This magnetic paint was applied onto a polyester film with a thickness of 12 μm to a dry thickness of about 3 μm, dried, surface treated, and then cut into a predetermined width to produce a magnetic tape.

Comparative Example 1 A cobalt-containing γ-Fe203 magnetic powder was obtained in the same manner as in Example 1, except that the surface treatment of the cobalt-containing γ-Fe203 magnetic powder was omitted in Example 1, and the cobalt-containing γ-Fe203 magnetic powder thus obtained was A magnetic tape was produced in the same manner as in Example 1, except that the same amount of -Fe203 magnetic powder was used in place of the cobalt-containing r-Fe203 magnetic powder used in Example 1.

Comparative Example 2 A cobalt-containing r-Fe203 magnetic powder was prepared in the same manner as in Example 1, except that the same amount of sodium dioctyl sulfosuccinate was used in place of Netrol 42 in the surface treatment of the cobalt-containing r-Fe203 magnetic powder in Example 1. In place of the cobalt-containing γ-Fe203 magnetic powder used in Example 1, the cobalt-containing γ-Fe203 magnetic powder was coated with 35μ/g of sodium dioctyl sulfosuccinate.
-Magnetic tapes were made in the same manner as in Example 1 except that the same amount of Fe203 magnetic powder was used.

Regarding the magnetic tapes obtained in Examples and Comparative Examples,
The output at 15 KHz, DC noise, and surface roughness of the magnetic layer were measured. The surface roughness of the magnetic layer was measured using a stylus type surface roughness meter, and the numerical value of the surface roughness was expressed as a center line average (C, L, A). The table below shows the results.

Table 11 As is clear from the above table, the magnetic tape obtained by the present invention (Example 1) has higher output and lower DC noise than conventional magnetic tapes (Comparative Examples 1 and 2). The surface roughness is small, which indicates that the magnetic recording medium obtained by the present invention has excellent dispersibility of magnetic powder, good surface smoothness of the magnetic layer, and excellent electrical properties.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. A magnetic recording medium containing a magnetic powder and a poly(acrylic acid-propylene glycol acrylate, ester)-based high molecular weight surfactant in the magnetic layer.